This study is designed to examine the effects of center and family day care of varying quality on the psychological development of one- and two-year-old children. The major questions of the study are: (1) Does center or family day care have an effect on child behavior such as response to frustration or adult-child interaction such as mother-child attachment? (2) Does family day care differ from center day care in its effects on child behaviors or adult-child interaction? (3) Does the age at which a child begins supplemental care make a difference in the effects of day care on the above variables? (4) Does the quality of day care as measured by amount and kind of caregiver-child interaction, make a difference in the effects of day care? (5) Do the effects of day care persist over the time and across different settings? The sample will be equally divided between boys and girls and will come from three ethnic backgrounds: 70% white, 15% Mexican-American, and 15% black. Socioeconomic status will vary from middle income families to very low income families dependent on Aid to Families with Dependent Children. Approximately 230 children between 12 and 24 months will be pretested before some enter day care, observed on six different occasions during a five-month period, and posttested at five months and again at eight months after pretesting. The children will be divided into four groups for analysis: (1) Center Day Care Group, (2) Family Day Care Group, (3) Unstable Care Group, and (4) Home-Reared Comparison Group. Allowing for attrition, there will be 50 children in each day care group, 30 in the unstable Care Group, and 100 children in the home-reared comparison. This study will provide information relevant to our understanding of the theory and nature of the relation between environmental experience and development. The findings from this study will therefore enhance our fundamental knowledge of child development and may be useful in social policy formulation.